1. Field of the Invention
The present invention relates to a method and apparatus for adjusting cooling in a projection system, and more particularly to a method and apparatus for adjusting cooling airflow.
2. Description of the Prior Art
A high power lamp is generally used as an illumination source in a projecting device. Although the high heat yielded from the lamp can be cooled through a fan, but the rotation noise caused from the high speed rotation of the fan always interference a meeting processing or spoil a silent sight amusement environment. As FIG. 1 shows, a lamp 12 is installed in a louver 12 of a conventional projection device 10. An illumination beam is projected from the lamp 12 and then through an optical system in the projection device 10 to form a beam with image information, and finally projected through a projecting lens to show pictures.
As FIG. 2 shows, a fan 14 is installed close to the lamp 12 in the projection device 10 to form an air current to cool the high temperature lamp 12. And, the cooling air passed through the high temperature lamp 12 is allowed to expel out the projection device 11 from the louver 11 installed close to the lamp 12. The louver 11, constructed to be a fixing type louver, consists of a plurality of parallel diversion plates 111 supported by a vertical supporting strip 112, and the diversion plates 111 are inclined downward properly so as to prevent diffusion light emitted from the lamp 12 from escaping out of the louver 11 to influence a projection effect.
However, this kind of the fixing type louver 11 facilitated with the downward inclined diversion plates 111 not only makes airflow to be diverted and then to flow out thereof with the result that the airflow resistance is yielded, but also causes the open area (open rate is approximately 40%) of the louver 11 to be shrunk. This reduces the effective cross-sectional area for hot air to be expelled and has no choice but increases the rotational speed of the fan in order to attain a cooling effect and consequently the noise caused from the fan is elevated and high rotational speed may damage the life of the fan. Besides, the fan with a high fixed rotational speed cannot match up with the operation condition of the projection device 10, the rotational speed of the fan and the effective open cross-sectional area are changed timely to allow the fan to be operated at a proper rotational speed to lessen the load thereof. And, the sudden shrinkage of the effective cross-sectional area of the fixing type louver 11 may also cause the speed of the airflow passed through it to be increased to form wind shear so as to yield noise to influence the broadcasting quality of the projection device.